If
the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule
13D, and is filing this schedule because of §§ 240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following
box ¨.

Note: Schedules
filed in paper format shall include a signed original and five copies of the schedule, including all exhibits. See
§ 240.13d-7 for other parties to whom copies are to be sent.

1
The remainder of this cover page shall be filled out for a reporting person’s initial filing on this form with respect to
the subject class of securities, and for any subsequent amendment containing information which would alter disclosures provided
in a prior cover page.

The information required
on the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities
Exchange Act of 1934 (“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject
to all other provisions of the Act (however, see the Notes).

CUSIP NO. 590328209

1

NAME OF REPORTING PERSON

JFL Partners Fund LP

2

CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

(a) ☒

(b) ☐

3

SEC USE ONLY

4

SOURCE OF FUNDS

WC

5

CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)

☐

6

CITIZENSHIP OR PLACE OF ORGANIZATION

DELAWARE

NUMBER OF

7

SOLE VOTING POWER

SHARES

BENEFICIALLY

485,026

OWNED BY

8

SHARED VOTING POWER

EACH

REPORTING

- 0 -

PERSON WITH

9

SOLE DISPOSITIVE POWER

485,026

10

SHARED DISPOSITIVE POWER

- 0 -

11

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

485,026

12

CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

☐

13

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

3.6%

14

TYPE OF REPORTING PERSON

PN

2

CUSIP NO. 590328209

1

NAME OF REPORTING PERSON

JFL Capital Management LP

2

CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

(a) ☒

(b) ☐

3

SEC USE ONLY

4

SOURCE OF FUNDS

OO

5

CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)

☐

6

CITIZENSHIP OR PLACE OF ORGANIZATION

TEXAS

NUMBER OF

7

SOLE VOTING POWER

SHARES

BENEFICIALLY

485,026

OWNED BY

8

SHARED VOTING POWER

EACH

REPORTING

- 0 -

PERSON WITH

9

SOLE DISPOSITIVE POWER

485,026

10

SHARED DISPOSITIVE POWER

- 0 -

11

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

485,026

12

CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

☐

13

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

3.6%

14

TYPE OF REPORTING PERSON

PN

3

CUSIP NO. 590328209

1

NAME OF REPORTING PERSON

JFL Capital Holdings LLC

2

CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

(a) ☒

(b) ☐

3

SEC USE ONLY

4

SOURCE OF FUNDS

OO

5

CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)

☐

6

CITIZENSHIP OR PLACE OF ORGANIZATION

DELAWARE

NUMBER OF

7

SOLE VOTING POWER

SHARES

BENEFICIALLY

485,026

OWNED BY

8

SHARED VOTING POWER

EACH

REPORTING

- 0 -

PERSON WITH

9

SOLE DISPOSITIVE POWER

485,026

10

SHARED DISPOSITIVE POWER

- 0 -

11

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

485,026

12

CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

☐

13

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

3.6%

14

TYPE OF REPORTING PERSON

OO

4

CUSIP NO. 590328209

1

NAME OF REPORTING PERSON

JFL Capital Management LLC

2

CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

(a) ☒

(b) ☐

3

SEC USE ONLY

4

SOURCE OF FUNDS

OO

5

CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)

☐

6

CITIZENSHIP OR PLACE OF ORGANIZATION

DELAWARE

NUMBER OF

7

SOLE VOTING POWER

SHARES

BENEFICIALLY

1,162,262

OWNED BY

8

SHARED VOTING POWER

EACH

REPORTING

- 0 -

PERSON WITH

9

SOLE DISPOSITIVE POWER

1,162,262

10

SHARED DISPOSITIVE POWER

- 0 -

11

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

1,162,262

12

CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

☐

13

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

8.7%

14

TYPE OF REPORTING PERSON

OO

5

CUSIP NO. 590328209

1

NAME OF REPORTING PERSON

Joseph F. Lawler

2

CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

(a) ☒

(b) ☐

3

SEC USE ONLY

4

SOURCE OF FUNDS

OO

5

CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)

☐

6

CITIZENSHIP OR PLACE OF ORGANIZATION

USA

NUMBER OF

7

SOLE VOTING POWER

SHARES

BENEFICIALLY

1,162,262

OWNED BY

8

SHARED VOTING POWER

EACH

REPORTING

- 0 -

PERSON WITH

9

SOLE DISPOSITIVE POWER

1,162,262

10

SHARED DISPOSITIVE POWER

- 0 -

11

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

1,162,262

12

CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

☐

13

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

8.7%

14

TYPE OF REPORTING PERSON

IN

6

CUSIP NO. 590328209

1

NAME OF REPORTING PERSON

22NW Fund, LP

2

CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

(a) ☒

(b) ☐

3

SEC USE ONLY

4

SOURCE OF FUNDS

WC

5

CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)

☐

6

CITIZENSHIP OR PLACE OF ORGANIZATION

DELAWARE

NUMBER OF

7

SOLE VOTING POWER

SHARES

BENEFICIALLY

1,092,263

OWNED BY

8

SHARED VOTING POWER

EACH

REPORTING

- 0 -

PERSON WITH

9

SOLE DISPOSITIVE POWER

1,092,263

10

SHARED DISPOSITIVE POWER

- 0 -

11

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

1,092,263

12

CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

☐

13

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

8.2%

14

TYPE OF REPORTING PERSON

PN

7

CUSIP NO. 590328209

1

NAME OF REPORTING PERSON

22NW, LP

2

CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

(a) ☒

(b) ☐

3

SEC USE ONLY

4

SOURCE OF FUNDS

OO

5

CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)

☐

6

CITIZENSHIP OR PLACE OF ORGANIZATION

DELAWARE

NUMBER OF

7

SOLE VOTING POWER

SHARES

BENEFICIALLY

1,092,263

OWNED BY

8

SHARED VOTING POWER

EACH

REPORTING

- 0 -

PERSON WITH

9

SOLE DISPOSITIVE POWER

1,092,263

10

SHARED DISPOSITIVE POWER

- 0 -

11

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

1,092,263

12

CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

☐

13

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

8.2%

14

TYPE OF REPORTING PERSON

PN

8

CUSIP NO. 590328209

1

NAME OF REPORTING PERSON

22NW Fund GP, LLC

2

CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

(a) ☒

(b) ☐

3

SEC USE ONLY

4

SOURCE OF FUNDS

OO

5

CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)

☐

6

CITIZENSHIP OR PLACE OF ORGANIZATION

DELAWARE

NUMBER OF

7

SOLE VOTING POWER

SHARES

BENEFICIALLY

1,092,263

OWNED BY

8

SHARED VOTING POWER

EACH

REPORTING

- 0 -

PERSON WITH

9

SOLE DISPOSITIVE POWER

1,092,263

10

SHARED DISPOSITIVE POWER

- 0 -

11

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

1,092,263

12

CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

☐

13

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

8.2%

14

TYPE OF REPORTING PERSON

OO

9

CUSIP NO. 590328209

1

NAME OF REPORTING PERSON

Aron R. English

2

CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

(a) ☒

(b) ☐

3

SEC USE ONLY

4

SOURCE OF FUNDS

OO

5

CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)

☐

6

CITIZENSHIP OR PLACE OF ORGANIZATION

USA

NUMBER OF

7

SOLE VOTING POWER

SHARES

BENEFICIALLY

1,092,263

OWNED BY

8

SHARED VOTING POWER

EACH

REPORTING

- 0 -

PERSON WITH

9

SOLE DISPOSITIVE POWER

1,092,263

10

SHARED DISPOSITIVE POWER

- 0 -

11

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

1,092,263

12

CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

☐

13

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

8.2%

14

TYPE OF REPORTING PERSON

IN

10

CUSIP NO. 590328209

1

NAME OF REPORTING PERSON

Jason M. Aryeh

2

CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

(a) ☒

(b) ☐

3

SEC USE ONLY

4

SOURCE OF FUNDS

5

CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)

☐

6

CITIZENSHIP OR PLACE OF ORGANIZATION

USA

NUMBER OF

7

SOLE VOTING POWER

SHARES

BENEFICIALLY

- 0 -

OWNED BY

8

SHARED VOTING POWER

EACH

REPORTING

- 0 -

PERSON WITH

9

SOLE DISPOSITIVE POWER

- 0 -

10

SHARED DISPOSITIVE POWER

- 0 -

11

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

- 0 -

12

CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

☐

13

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

0%

14

TYPE OF REPORTING PERSON

IN

11

CUSIP NO. 590328209

1

NAME OF REPORTING PERSON

Kenneth Lin

2

CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

(a) ☒

(b) ☐

3

SEC USE ONLY

4

SOURCE OF FUNDS

PF

5

CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)

☐

6

CITIZENSHIP OR PLACE OF ORGANIZATION

USA

NUMBER OF

7

SOLE VOTING POWER

SHARES

BENEFICIALLY

5,000

OWNED BY

8

SHARED VOTING POWER

EACH

REPORTING

- 0 -

PERSON WITH

9

SOLE DISPOSITIVE POWER

5,000

10

SHARED DISPOSITIVE POWER

- 0 -

11

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

5,000

12

CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

☐

13

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

Less than 1%

14

TYPE OF REPORTING PERSON

IN

12

CUSIP NO. 590328209

The following constitutes
Amendment No. 2 to the Schedule 13D filed by the undersigned (“Amendment No. 2”). This Amendment No. 2 amends the Schedule
13D as specifically set forth herein. 22NW, LP previously filed a Schedule 13G with the Securities and Exchange Commission on February
8, 2019 with respect to securities of the Issuer.

Joseph F. Lawler, M.D., Ph.D., as the Managing Member of each of JFL Holdings and JFL Capital Management;

(vi)

22NW Fund, LP, a Delaware limited partnership (“22NW Fund”), with respect to the Shares
directly and beneficially owned by it;

(vii)

22NW, LP, a Delaware limited partnership (“22NW”), as the general partner and investment
adviser to 22NW Fund;

(viii)

22NW Fund GP, LLC, a Delaware limited liability company (“22NW GP”), as the general
partner of 22NW;

(ix)

Aron R. English, as the Portfolio Manager of 22NW and Managing Member of 22NW GP;

(x)

Jason M. Aryeh; and

(xi)

Kenneth Lin, M.D.

Each of the foregoing
is referred to as a “Reporting Person” and collectively as the “Reporting Persons.” Each of the Reporting
Persons is party to that certain Joint Filing and Solicitation Agreement, as further described in Item 6. Accordingly, the Reporting
Persons are hereby filing a joint Schedule 13D.

13

CUSIP NO. 590328209

(b) The
address of the principal office of each of JFL Partners, JFL GP, JFL Holdings, JFL Capital Management and Dr. Lawler is 2110 Ranch
Road 620 S, #341732, Lakeway, Texas 78734. The address of the principal office of each of 22NW Fund, 22NW, 22NW GP and Mr. English
is 1455 NW Leary Way, Suite 400, Seattle, Washington 98107. The address of the principal office of Mr. Aryeh is 34 Sumner Road,
Greenwich, Connecticut 06831. The address of the principal office of Dr. Lin is 280 Utah Avenue, Suite 250, South San Francisco,
California 94080.

(c) The
principal business of JFL Partners is investing in securities. The principal business of JFL GP is serving as the general partner
of JFL Partners. The principal business of JFL Holdings is serving as the general partner of JFL GP. The principal business of
JFL Capital Management is serving as the investment manager of JFL Partners and the JFL Account. Dr. Lawler is the Managing Member
of each of JFL Holdings and JFL Capital Management. The principal business of 22NW Fund is investing in securities. The principal
business of 22NW is serving as the general partner and investment adviser to 22NW Fund. The principal business of 22NW GP is serving
as the general partner of 22NW. Mr. English is the Portfolio Manager of 22NW and Managing Member of 22NW GP. The principal occupation
of Mr. Aryeh is serving as the Managing General Partner of JALAA Equities, LP, a private investment fund focused on the biotechnology
and medical device sectors. The principal occupation of Dr. Lin is serving as the Chief Executive Officer and President of Ab Initio
Biotherapeutics Inc., a biologics discovery company focusing on G-protein coupled receptors.

(d) No
Reporting Person has, during the last five years, been convicted in a criminal proceeding (excluding traffic violations or similar
misdemeanors).

(e) No
Reporting Person has, during the last five years, been party to a civil proceeding of a judicial or administrative body of competent
jurisdiction and as a result of such proceeding was or is subject to a judgment, decree or final order enjoining future violations
of, or prohibiting or mandating activities subject to, federal or state securities laws or finding any violation with respect to
such laws.

(f) JFL
Partners, JFL Holdings, JFL Capital Management, 22NW Fund, 22NW and 22NW GP are organized under the laws of the State of Delaware.
JFL GP is organized under the laws of the State of Texas. Dr. Lawler, Mr. English, Mr. Aryeh and Dr. Lin are citizens of the United
States of America.

Item 3.

Source and Amount of Funds or Other Consideration.

Item 3 is hereby amended
and restated to read as follows:

The Shares purchased
by JFL Partners and held in the JFL Account were purchased with working capital (which may, at any given time, include margin loans
made by brokerage firms in the ordinary course of business). The aggregate purchase price of the 485,026 Shares beneficially owned
by JFL Partners is approximately $1,964,750, including brokerage commissions. The aggregate purchase price of the 677,236 Shares
held in the JFL Account is approximately $2,710,311, including brokerage commissions.

The Shares purchased
by 22NW Fund were purchased with working capital (which may, at any given time, include margin loans made by brokerage firms in
the ordinary course of business). The aggregate purchase price of the 1,092,263 Shares beneficially owned by 22NW Fund is approximately
$4,933,677, including brokerage commissions.

The Shares purchased
by Dr. Lin were purchased with personal funds (which may, at any given time, include margin loans made by brokerage firms in the
ordinary course of business). The aggregate purchase price of the 5,000 Shares directly owned by Dr. Lin is approximately $20,350,
including brokerage commissions.

14

CUSIP NO. 590328209

Item 4.

Purpose of Transaction.

Item 4 is hereby amended
to add the following:

On March 13, 2019,
JFL Partners delivered a letter to the Issuer nominating Jason M. Aryeh, Aron R. English, Joseph F. Lawler, M.D., Ph.D., and Kenneth
Lin, M.D. (the “Nominees”) for election to the Board of Directors of the Issuer at the 2019 annual meeting of stockholders
(the “Annual Meeting”).

Item 5.

Interest in Securities of the Issuer.

Items 5(a) –
(c) are hereby amended and restated to read as follows:

(a) The
aggregate percentage of Shares reported owned by each person named herein is based upon 13,342,784 Shares outstanding as of February
27, 2019, which is the total number of Shares outstanding as reported in the Issuer’s annual report on Form 10-K filed with
the Securities and Exchange Commission on March 6, 2019.

As of the close of
business on March 13, 2019, JFL Partners directly beneficially owned 485,026 Shares, constituting approximately 3.6% of the Shares
outstanding. JFL GP, as the general partner of JFL Partners, may be deemed to beneficially own the 485,026 Shares owned by JFL
Partners, constituting approximately 3.6% of the Shares outstanding. JFL Holdings, as the general partner of JFL GP, may be deemed
to beneficially own the 485,026 Shares owned by JFL Partners, constituting approximately 3.6% of the Shares outstanding.

As of the close of
business on March 13, 2019, 677,236 Shares were held in the JFL Account, constituting approximately 5.1% of the Shares outstanding.

JFL Capital Management,
as the investment manager of JFL Partners and the JFL Account, may be deemed to beneficially own the 1,162,262 Shares owned in
the aggregate by JFL Partners and held in the JFL Account, constituting approximately 8.7% of the Shares outstanding. Dr. Lawler,
as the Managing Member of JFL Capital Management and JFL Holdings, may be deemed to beneficially own the 1,162,262 Shares owned
in the aggregate by JFL Partners and held in the JFL Account, constituting approximately 8.7% of the Shares outstanding.

As of the close of
business on March 13, 2019, 22NW Fund directly beneficially owned 1,092,263 Shares, constituting approximately 8.2% of the Shares
outstanding. 22NW, as the general partner and investment adviser to 22NW Fund, may be deemed to beneficially own the 1,092,263
Shares owned by 22NW Fund, constituting approximately 8.2% of the Shares outstanding. 22NW GP, as the general partner of 22NW,
may be deemed to beneficially own the 1,092,263 Shares owned by 22NW Fund, constituting approximately 8.2% of the Shares outstanding.
Mr. English, as the Portfolio Manager of 22NW and Managing Member of 22NW GP, may be deemed to beneficially own the 1,092,263 Shares
owned by 22NW Fund, constituting approximately 8.2% of the Shares outstanding.

As of the close of
business on March 13, 2019, Dr. Lin directly beneficially owned 5,000 Shares, constituting less than 1% of the Shares outstanding.

As of the close of
business on March 13, 2019, Mr. Aryeh did not beneficially own any Shares, constituting 0% of the Shares outstanding.

15

CUSIP NO. 590328209

An aggregate of 2,259,525
Shares, constituting approximately 16.9% of the Shares outstanding, are reported in this Amendment No. 2 to the Schedule 13D.

Each Reporting Person
may be deemed to be a member of a “group” with the other Reporting Persons for the purposes of Section 13(d)(3) of
the Securities Exchange Act of 1934, as amended, and such group may be deemed to beneficially own the 2,259,525 Shares owned in
the aggregate by all of the Reporting Persons. Each Reporting Person disclaims beneficial ownership of the Shares that he or it
does not directly own.

(b) By
virtue of their respective positions with JFL Partners, each of JFL GP, JFL Holdings, JFL Capital Management and Dr. Lawler may
be deemed to have sole power to vote and dispose of the Shares reported owned by JFL Partners.

By virtue of their
respective positions with the JFL Account, each of JFL Capital Management and Dr. Lawler may be deemed to have sole power to vote
and dispose of the Shares held in the JFL Account.

By virtue of their
respective positions with 22NW Fund, each of 22NW, 22NW GP and Mr. English may be deemed to have sole power to vote and dispose
of the Shares reported owned by 22NW Fund.

Dr. Lin has the sole
power to vote and dispose of the Shares directly beneficially owned by him.

(c) Schedule
A annexed hereto lists all transactions in securities of the Issuer by the Reporting Persons during the past 60 days. All of such
transactions were effected in the open market.

Item 6.

Contracts, Arrangements, Understandings or Relationships With Respect to Securities of the Issuer.

Item 6 is hereby amended
to add the following:

On March 13, 2019,
the Reporting Persons entered into a Joint Filing and Solicitation Agreement pursuant to which, among other things, the parties
agreed to (a) the joint filing on behalf of each of them of statements on Schedule 13D, and any amendments thereto, with respect
to the securities of the Issuer and (b) solicit proxies for the election of the Nominees at the Annual Meeting. A copy of the Joint
Filing and Solicitation Agreement is attached hereto as Exhibit 99.1 and is incorporated herein by reference.

Other than as described
herein, there are no contracts, arrangements, understandings or relationships among the Reporting Persons, or between the Reporting
Persons and any other person, with respect to the securities of the Issuer.

Item 7.

Material to be Filed as Exhibits.

Item 7 is hereby amended
to add the following exhibits:

99.1

Joint Filing and Solicitation Agreement, dated March 13, 2019.

99.2

Powers of Attorney.

16

CUSIP NO. 590328209

SIGNATURES

After reasonable inquiry
and to the best of his knowledge and belief, the undersigned certifies that the information set forth in this statement is true,
complete and correct.

Dated: March 14, 2019

JFL PARTNERS FUND LP

By:

JFL Capital Management LP
General Partner

By:

JFL Capital Holdings LLC
General Partner

By:

/s/ Joseph F. Lawler

Name:

Joseph F. Lawler

Title:

Managing Member

JFL CAPITAL MANAGEMENT LP

By:

JFL Capital Holdings LLC
General Partner

By:

/s/ Joseph F. Lawler

Name:

Joseph F. Lawler

Title:

Managing Member

JFL CAPITAL HOLDINGS LLC

By:

/s/ Joseph F. Lawler

Name:

Joseph F. Lawler

Title:

Managing Member

JFL CAPITAL MANAGEMENT LLC

By:

/s/ Joseph F. Lawler

Name:

Joseph F. Lawler

Title:

Managing Member

/s/ Joseph F. Lawler

JOSEPH F. LAWLER

Individually and as attorney-in-fact for Jason M. Aryeh and Kenneth
Lin

17

CUSIP NO. 590328209

22NW FUND, LP

By:

22NW, LP
General Partner and Investment Adviser

By:

22NW Fund GP, LLC
General Partner

By:

/s/ Aron R. English

Name:

Aron R. English

Title:

Managing Member

22NW, LP

By:

22NW Fund GP, LLC
General Partner

By:

/s/ Aron R. English

Name:

Aron R. English

Title:

Managing Member

22NW FUND GP, LLC

By:

/s/ Aron R. English

Name:

Aron R. English

Title:

Managing Member

/s/ Aron R. English

ARON R. ENGLISH

18

CUSIP NO. 590328209

SCHEDULE A

Transactions in Securities of
the Issuer During the Past 60 Days

Nature of the Transaction

Securities

Purchased/(Sold)

Price Per

Share($)

Date of

Purchase/Sale

JFL PARTNERS FUND LP

Sale of Common Stock

(100)

6.0200

02/14/2019

Sale of Common Stock

(2,412)

5.9452

02/15/2019

JFL CAPITAL MANAGEMENT LLC
(Through the JFL Account)

Sale of Common Stock

(3,469)

5.9452

02/15/2019

22NW FUND, LP

Purchase of Common Stock

6,071

4.9963

01/22/2019

Purchase of Common Stock

100

5.2500

01/30/2019

Purchase of Common Stock

240,000

5.8000

02/06/2019

Purchase of Common Stock

5,038

6.1803

03/06/2019

Purchase of Common Stock

900

6.2494

03/07/2019

Purchase of Common Stock

607

6.2475

03/08/2019

Purchase of Common Stock

200

6.2350

03/11/2019

Exhibit 99.1

JOINT FILING AND SOLICITATION AGREEMENT

WHEREAS, certain
of the undersigned are stockholders, direct or beneficial, of Merrimack Pharmaceuticals, Inc., a Delaware corporation (the “Company”);

WHEREAS, JFL
Partners Fund LP, JFL Capital Management LP, JFL Capital Holdings LLC, JFL Capital Management LLC and Joseph F. Lawler (together,
“JFL Capital”), 22NW Fund, LP, 22NW, LP, 22NW Fund GP, LLC and Aron R. English (together, “22NW”), Jason
M. Aryeh and Kenneth Lin wish to form a group for the purpose of seeking representation on the Board of Directors of the
Company (the “Board”) at the 2019 annual meeting of stockholders of the Company (including any other meeting of stockholders
held in lieu thereof, and any adjournments, postponements, reschedulings or continuations thereof, the “2019 Annual Meeting”)
and for the purpose of taking all other action necessary to achieve the foregoing.

NOW, IT IS AGREED,
this 13th day of March 2019 by the parties hereto:

1. In
accordance with Rule 13d-1(k)(1)(iii) under the Securities Exchange Act of 1934, as amended (the “Exchange Act”), each
of the undersigned (collectively, the “Group”) agrees to the joint filing on behalf of each of them of statements on
Schedule 13D, and any amendments thereto,
with respect to the securities of the Company. Each member of the Group shall be responsible
for the accuracy and completeness of its own disclosure therein, and is not responsible for the accuracy and completeness of the
information concerning the other members, unless such member knows or has reason to know that such information is inaccurate.

2. So
long as this agreement is in effect, each of the undersigned shall provide written notice to Olshan Frome Wolosky LLP (“Olshan”),
such notice to be given no later than four (4) hours after each such transaction, of (i) any of their purchases or sales of securities
of the Company or (ii) any securities of the Company over which they acquire or dispose of beneficial ownership; provided,
however, that while this agreement is in effect, no party hereto shall (i) buy, or increase any beneficial ownership
over, any securities of the Company if, as a result of such action, the Group would beneficially own more than 9.9% of the Company’s
outstanding common stock or (ii) sell, or dispose of any beneficial ownership over, any securities of the Company, in each case
without the prior consent of JFL Capital. For purposes of this agreement, the term “beneficial ownership” shall have
the meaning of such term set forth in Rule 13d-3 under the Exchange Act.

3. Each
of the undersigned agrees to form the Group for the purpose of (i) soliciting proxies for the election of the persons nominated
by JFL Capital to the Board at the 2019 Annual Meeting, (ii) taking such other actions as the parties deem advisable and (iii)
taking all other action necessary or advisable to achieve the foregoing.

4. JFL
Capital shall have the right to pre-approve all expenses incurred in connection with the Group’s activities and JFL Capital
agrees to pay directly all such pre-approved expenses; provided, however, that notwithstanding the
forgoing, 22NW shall be responsible for, and agrees to pay directly, all expenses and costs incurred in connection with (i) any
Forms 3 or 4 required to be filed by 22NW under Section 16(a) of the Exchange Act and (ii) any other filings that 22NW is separately
required to make with the Securities and Exchange Commission.

5. Each
of the undersigned agrees that any filing with the Securities and Exchange Commission, press release or stockholder communication
proposed to be made or issued by the Group or any member of the Group in connection with the Group’s activities set forth
in Section 3 shall be as directed by JFL Capital.

6. The
relationship of the parties hereto shall be limited to carrying on the business of the Group in accordance with the terms of this
agreement. Such relationship shall be construed and deemed to be for the sole and limited purpose of carrying on such business
as described herein. Nothing herein shall be construed to authorize any party to act as an agent for any other party, or to create
a joint venture or partnership, or to constitute an indemnification. Nothing herein shall restrict any party’s right to purchase
or sell securities of the Company, as it deems appropriate, in its sole discretion, provided that all such purchases and sales
are made in compliance with all applicable securities laws and the provisions of this agreement.

7. This
agreement may be executed in counterparts, each of which shall be deemed an original and all of which, taken together, shall constitute
but one and the same instrument, which may be sufficiently evidenced by one counterpart.

8. This
agreement is governed by and will be construed in accordance with the laws of the State of New York. In the event of any dispute
arising out of the provisions of this agreement or their investment in the Company, the parties hereto consent and submit to the
exclusive jurisdiction of the United States District Court for the Southern District of New York located in the Borough of Manhattan
or the courts of the State of New York located in the County of New York.

9. The
parties’ rights and obligations under this agreement (other than the rights and obligations set forth in Section 4 (solely
with respect to expenses incurred prior to the termination of the agreement) and Section 8 which shall survive any termination
of this agreement) shall terminate immediately after the conclusion of the activities set forth in Section 3 or as otherwise agreed
to by the parties. Notwithstanding the foregoing, any party hereto may terminate its obligations under this agreement on 24 hours’
written notice to all other parties, with a copy by fax to Steve Wolosky and Ryan Nebel at Olshan, Fax No. (212) 451-2222.

10. Each
party acknowledges that Olshan shall act as counsel for both the Group and JFL Capital relating to their investment in the Company.

11. Each
of the undersigned parties hereby agrees that this agreement shall be filed as an exhibit to a Schedule 13D pursuant to Rule 13d-1(k)(1)(iii)
under the Exchange Act.

IN WITNESS WHEREOF, the parties hereto
have caused this agreement to be executed as of the day and year first above written.

JFL PARTNERS FUND LP

By:

JFL Capital Management LP
General Partner

By:

JFL Capital Holdings LLC
General Partner

By:

/s/ Joseph F. Lawler

Name:

Joseph F. Lawler

Title:

Managing Member

JFL CAPITAL MANAGEMENT LP

By:

JFL Capital Holdings LLC
General Partner

By:

/s/ Joseph F. Lawler

Name:

Joseph F. Lawler

Title:

Managing Member

JFL CAPITAL HOLDINGS LLC

By:

/s/ Joseph F. Lawler

Name:

Joseph F. Lawler

Title:

Managing Member

JFL CAPITAL MANAGEMENT LLC

By:

/s/ Joseph F. Lawler

Name:

Joseph F. Lawler

Title:

Managing Member

/s/ Joseph F. Lawler

JOSEPH F. LAWLER

22NW FUND, LP

By:

22NW, LP
General Partner and Investment Adviser

By:

22NW Fund GP, LLC
General Partner

By:

/s/ Aron R. English

Name:

Aron R. English

Title:

Managing Member

22NW, LP

By:

22NW Fund GP, LLC
General Partner

By:

/s/ Aron R. English

Name:

Aron R. English

Title:

Managing Member

22NW FUND GP, LLC

By:

/s/ Aron R. English

Name:

Aron R. English

Title:

Managing Member

/s/ Aron R. English

ARON R. ENGLISH

/s/ Jason M. Aryeh

JASON M. ARYEH

/s/ Kenneth Lin

KENNETH LIN

Exhibit 99.2

POWER OF ATTORNEY

Know all by these
presents, that the undersigned hereby constitutes and appoints Joseph F. Lawler the undersigned’s true and lawful attorney-in-fact
to take any and all action in connection with (i) the undersigned’s beneficial ownership of, or participation in a group
with respect to, securities of Merrimack Pharmaceuticals, Inc., a Delaware corporation (the “Company”), directly or
indirectly beneficially owned by JFL Partners Fund LP or any of its affiliates (collectively, the “Group”), and (ii)
any proxy solicitation of the Group to elect the Group’s slate of director nominees to the board of directors of the Company
at the 2019 annual meeting of stockholders of the Company (the “Solicitation”). Such action shall include, but not
be limited to:

1.executing for and on behalf of the undersigned any Schedule 13D, and amendments thereto, filed by the Group that
are required to be filed under Section 13(d) of the Securities Exchange Act of 1934, as amended (the “Exchange Act”),
and the rules thereunder in connection with the undersigned’s beneficial ownership of, or participation in a group with respect
to, securities of the Company or the Solicitation;

2.if applicable, executing for
and on behalf of the undersigned all Forms 3, 4 and 5 required to be filed under Section
16(a) of the Exchange Act in connection with the undersigned’s beneficial ownership of, or participation in a group with
respect to, securities of the Company or the Solicitation;

3.executing for and on behalf of the undersigned all Joint Filing and Solicitation Agreements or similar documents
pursuant to which the undersigned shall agree to be a member of the Group;

4.performing any and all acts for and on behalf of the undersigned that may be necessary or desirable to complete and
execute any such document, complete and execute any amendment or amendments thereto, and timely file such form with the United
States Securities and Exchange Commission and any stock exchange or similar authority; and

5.taking any other action of any type whatsoever in connection with the Solicitation, including entering into any settlement
agreement, that in the opinion of such attorney-in-fact, may be of benefit to, in the best interest of, or legally required by,
the undersigned, it being understood that the documents executed by such attorney-in-fact on behalf of the undersigned pursuant
to this Power of Attorney shall be in such form and shall contain such terms and conditions as such attorney-in-fact may approve
in such attorney-in-fact’s discretion.

The undersigned
hereby grants to such attorney-in-fact full power and authority to do and perform any and every act and thing whatsoever requisite,
necessary, or proper to be done in the exercise of any of the rights and powers herein granted, as fully to all intents and purposes
as the undersigned might or could do if personally present, with full power of substitution or revocation, hereby ratifying and
confirming all that such attorney-in-fact, or such attorney-in-fact’s substitutes, shall lawfully do or cause to be done
by virtue of this Power of Attorney and the rights and powers herein granted. The undersigned acknowledges that the foregoing attorney-in-fact,
in serving in such capacity at the request of the undersigned, is not assuming any of the undersigned’s responsibilities
to comply with Section 13(d), Section 16 or Section 14 of the Exchange Act.

This Power of Attorney
shall remain in full force and effect until the undersigned is no longer a member of the Group unless earlier revoked by the undersigned
in a signed writing delivered to the foregoing attorney-in-fact.

IN WITNESS WHEREOF,
the undersigned has caused this Power of Attorney to be executed as of this 13th day of March 2019.

/s/ Jason M. Aryeh

JASON M. ARYEH

POWER OF ATTORNEY

Know all by these
presents, that the undersigned hereby constitutes and appoints Joseph F. Lawler the undersigned’s true and lawful attorney-in-fact
to take any and all action in connection with (i) the undersigned’s beneficial ownership of, or participation in a group
with respect to, securities of Merrimack Pharmaceuticals, Inc., a Delaware corporation (the “Company”), directly or
indirectly beneficially owned by JFL Partners Fund LP or any of its affiliates (collectively, the “Group”), and (ii)
any proxy solicitation of the Group to elect the Group’s slate of director nominees to the board of directors of the Company
at the 2019 annual meeting of stockholders of the Company (the “Solicitation”). Such action shall include, but not
be limited to:

1.executing for and on behalf of the undersigned any Schedule 13D, and amendments thereto, filed by the Group that
are required to be filed under Section 13(d) of the Securities Exchange Act of 1934, as amended (the “Exchange Act”),
and the rules thereunder in connection with the undersigned’s beneficial ownership of, or participation in a group with respect
to, securities of the Company or the Solicitation;

2.if applicable, executing for and on behalf of the undersigned all Forms 3, 4 and 5 required to be filed under Section
16(a) of the Exchange Act in connection with the undersigned’s beneficial ownership of, or participation in a group with
respect to, securities of the Company or the Solicitation;

3.executing for and on behalf of the undersigned all Joint Filing and Solicitation Agreements or similar documents
pursuant to which the undersigned shall agree to be a member of the Group;

4.performing any and all acts for and on behalf of the undersigned that may be necessary or desirable to complete and
execute any such document, complete and execute any amendment or amendments thereto, and timely file such form with the United
States Securities and Exchange Commission and any stock exchange or similar authority; and

5.taking any other action of any type whatsoever in connection with the Solicitation, including entering into any settlement
agreement, that in the opinion of such attorney-in-fact, may be of benefit to, in the best interest of, or legally required by,
the undersigned, it being understood that the documents executed by such attorney-in-fact on behalf of the undersigned pursuant
to this Power of Attorney shall be in such form and shall contain such terms and conditions as such attorney-in-fact may approve
in such attorney-in-fact’s discretion.

The undersigned
hereby grants to such attorney-in-fact full power and authority to do and perform any and every act and thing whatsoever requisite,
necessary, or proper to be done in the exercise of any of the rights and powers herein granted, as fully to all intents and purposes
as the undersigned might or could do if personally present, with full power of substitution or revocation, hereby ratifying and
confirming all that such attorney-in-fact, or such attorney-in-fact’s substitutes, shall lawfully do or cause to be done
by virtue of this Power of Attorney and the rights and powers herein granted. The undersigned acknowledges that the foregoing attorney-in-fact,
in serving in such capacity at the request of the undersigned, is not assuming any of the undersigned’s responsibilities
to comply with Section 13(d), Section 16 or Section 14 of the Exchange Act.

This Power of Attorney
shall remain in full force and effect until the undersigned is no longer a member of the Group unless earlier revoked by the undersigned
in a signed writing delivered to the foregoing attorney-in-fact.

IN WITNESS WHEREOF,
the undersigned has caused this Power of Attorney to be executed as of this 13th day of March 2019.

/s/ Aron R. English

ARON R. ENGLISH

POWER OF ATTORNEY

Know all by
these presents, that the undersigned hereby constitutes and appoints Joseph F. Lawler the undersigned’s true and lawful attorney-in-fact
to take any and all action in connection with (i) the undersigned’s beneficial ownership of, or participation in a group
with respect to, securities of Merrimack Pharmaceuticals, Inc., a Delaware corporation (the “Company”), directly or
indirectly beneficially owned by JFL Partners Fund LP or any of its affiliates (collectively, the “Group”), and (ii)
any proxy solicitation of the Group to elect the Group’s slate of director nominees to the board of directors of the Company
at the 2019 annual meeting of stockholders of the Company (the “Solicitation”). Such action shall include, but not
be limited to:

1.executing for and on behalf of the undersigned any Schedule 13D, and amendments thereto, filed by the Group that
are required to be filed under Section 13(d) of the Securities Exchange Act of 1934, as amended (the “Exchange Act”),
and the rules thereunder in connection with the undersigned’s beneficial ownership of, or participation in a group with respect
to, securities of the Company or the Solicitation;

2.if applicable, executing for and on behalf of the undersigned all Forms 3, 4 and 5 required to be filed under Section
16(a) of the Exchange Act in connection with the undersigned’s beneficial ownership of, or participation in a group with
respect to, securities of the Company or the Solicitation;

3.executing for and on behalf of the undersigned all Joint Filing and Solicitation Agreements or similar documents
pursuant to which the undersigned shall agree to be a member of the Group;

4.performing any and all acts for and on behalf of the undersigned that may be necessary or desirable to complete and
execute any such document, complete and execute any amendment or amendments thereto, and timely file such form with the United
States Securities and Exchange Commission and any stock exchange or similar authority; and

5.taking any other action of any type whatsoever in connection with the Solicitation, including entering into any settlement
agreement, that in the opinion of such attorney-in-fact, may be of benefit to, in the best interest of, or legally required by,
the undersigned, it being understood that the documents executed by such attorney-in-fact on behalf of the undersigned pursuant
to this Power of Attorney shall be in such form and shall contain such terms and conditions as such attorney-in-fact may approve
in such attorney-in-fact’s discretion.

The undersigned
hereby grants to such attorney-in-fact full power and authority to do and perform any and every act and thing whatsoever requisite,
necessary, or proper to be done in the exercise of any of the rights and powers herein granted, as fully to all intents and purposes
as the undersigned might or could do if personally present, with full power of substitution or revocation, hereby ratifying and
confirming all that such attorney-in-fact, or such attorney-in-fact’s substitutes, shall lawfully do or cause to be done
by virtue of this Power of Attorney and the rights and powers herein granted. The undersigned acknowledges that the foregoing attorney-in-fact,
in serving in such capacity at the request of the undersigned, is not assuming any of the undersigned’s responsibilities
to comply with Section 13(d), Section 16 or Section 14 of the Exchange Act.

This Power of Attorney
shall remain in full force and effect until the undersigned is no longer a member of the Group unless earlier revoked by the undersigned
in a signed writing delivered to the foregoing attorney-in-fact.

IN WITNESS WHEREOF,
the undersigned has caused this Power of Attorney to be executed as of this 13th day of March 2019.